In recent years, the popularity and growth of wireless communication networks has increased in dramatic fashion. In fact, wireless networks are continually pressed to keep up with the demands for increased capacity while maintaining reliable and acceptable service. Steps are continuously being taken to increase capacity in existing networks, but the demand for more capacity remains because of the tremendous growth in wireless communications.
Traditional wireless communication networks are partitioned into service areas known as cells wherein mobile units within a cell communicate via radio links with a base station that services that cell. The base station is coupled to the public switch telephone network: for access to the land network. A pool of available frequency channels is assigned to each cell in such a way that the same frequency channels can be reused in other cells that are sufficiently separated by enough distance to prevent unacceptable co-channel interference. These frequency channel re-use patterns can be implemented with assumptions that include equal-sized, regularly spaced cells with uniformly distributed traffic loads. The re-use patterns can also be adjusted to increase capacity based on real world considerations such as usage patterns and topography to increase capacity. The design and operation of a typical wireless communication network is described in an article titled “Advanced Mobile Phone Service” by Belcher, IEEE Transactions on Vehicular Technology, Vol. VT29, No. 2, May 1980, pp. 238–244.
Attempts at further increasing capacity for digital wireless networks have included using a Code Division Multiple Access (CDMA) architecture based on the IS-95 digital wireless standard. IS-95 refers to the standard set by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA) for the implementation of a CDMA architecture. In CDMA systems, a unique code is allocated to each mobile unit and all calls are communicated simultaneously over a broad band of frequency, i.e., 1.25 MHz for IS-95, thus spreading the energy of the calls over a large bandwidth. The calls are decoded by using the knowledge of the unique code of a mobile unit to retrieve a particular call.
Further attempts to increase capacity for wireless communication networks have been implemented by using a Time Division Multiple Access (TDMA) architecture. TDMA is an implementation that allows multiple calls to use a shared frequency channel by using different time slots. Standards have been set by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA) for the implementation of a TDMA architecture following EIA/TIA documents IS-54/IS-136. The European digital wireless network, referred to as Global System for Mobile Communications (GSM), also uses a TDMA architecture. The frequency channel is divided into timeslots with each mobile unit being assigned at least one timeslot during which it can communicate with the base station. For IS-54/IS-136 each frequency channel is allocated 30 kHz of bandwidth which is divided into six timeslots. For full rate operation, each mobile unit is assigned two of the six timeslots of the frequency channel. For half rate operation, each mobile unit is assigned only one timeslot.
A technique to increase capacity over traditional TDMA is called Enhanced Time Division Multiple Access (E-TDMA) which dynamically allocates timeslots to mobile units thereby taking advantage of the dead space that results from one-way alternating conversations and the redundant nature of human speech. Accordingly, mobile units are not assigned permanent timeslots for the call duration but receive timeslots for communicating only when needed. However, E-TDMA is complex in design, and therefore, difficult if not impractical to implement. The cost of an E-TDMA system is yet another impediment to its acceptance.
The growth of existing wireless communication networks is threatened by the capacity restraints of the networks. The use of more cells is costly because of the additional base stations needed and the problems of securing additional base station sites. Also, many existing wireless communication providers are already heavily invested in equipment for specific architectures so converting to another architecture is not a commercially viable option. Therefore, it would be desirable to be able to further increase capacity efficiently, economically, and without degrading service of existing wireless communication networks. It is also desirable to give new wireless communication providers a broader array of choices when equipment and capacity concerns are addressed.